Environmental concerns and governmental regulations require reduced emissions of volatile hydrocarbon fuel vapors into the atmosphere. One source of hydrocarbon fuel vapors is fuel tanks of vehicles using gasoline or other hydrocarbon fuels with high volatility. Fuel vapor can escape to the atmosphere during the filling of the tanks and usually, even after the tanks are filled. The use of an onboard vapor recovery system to remove excess fuel vapor from the fuel tank is one solution to the problem. Typically, a canister with activated charcoal therein receives fuel vapors through a valve assembly mounted in the top of the fuel tank and communicates with the intake manifold of the vehicle engine for withdrawing fuel vapor from the canister during operation of the engine. The valve assembly may have a valve responsive to the level of fuel in the tank that enables the valves to stay open at a sufficiently low fuel level to permit fuel vapors to flow from the fuel tank into the canister. As the fuel level rises during filling to approach a desired maximum fuel level or quantity of fuel in the tank, a float is raised to close the valve to prevent liquid fuel from flowing through the valve and into the vapor canister. The closed valve also prevents fuel vapor from flowing into the vapor canister. One such system is disclosed in U.S. Pat. No. 5,579,802.
Some of these systems require a high capacity or high flow rate to control the flow of vapor from the fuel tank to the vapor storage canister. Current high capacity or high flow rate valve designs tend to be forced into and held in a closed position, when they should be open, by the vapor pressure in the fuel tank. This prevents vapor from flowing through the valve and into the vapor storage canister defeating the purpose of the system. Further, prior fuel level and vapor vent valves utilize a single float responsive to the fuel level in the fuel tank to close the valve. This single float arrangement maintains the valve closed while the fuel level remains at or near the desired maximum level of fuel in the tank to limit the amount of liquid fuel which undesirably escapes through the valve. Maintaining the valve closed while the fuel level remains at or near the maximum level of fuel in the tank is undesirable because the addition of fuel to the tank when the valve is closed will increase the pressure within the tank and increase the discharge of hydrocarbon fuel vapors into the atmosphere.
Further, when a vehicle stops, turns rapidly or is travelling across rough terrain significant splashing or sloshing of fuel in the fuel tank can occur. It has been found that the splashing and sloshing of fuel in the tank is particularly bad when the tank is between 1/4+L and 3/4+L full. Conventional vapor vent valves permit an undesirable amount of liquid fuel to escape from the fuel tank through the vent valve whereupon it flows to the fuel vapor canister which has a limited volume and storage capacity and is rapidly filled by liquid fuel. Typically, the liquid fuel escapes from conventional vent valves because the outlet thereof is not adequately protected from sloshing or splashing fuel and the valve closure mechanism is not responsive enough to rapidly close the valve and prevent such liquid fuel escape.
Typical vapor vent valves are mounted within an opening through the vehicle fuel tank, and a fuel pump is mounted through a separate opening in the fuel tank. Additional openings through the fuel tank may be provided to mount additional components such as an overpressure relief valve and the like. Each opening through the fuel tank provides a leak path through which hazardous hydrocarbon fuel vapors may escape to the atmosphere.